ARBs work similarly to ACE inhibitors in that they both reduce blood pressure by acting on the renin-angiotensin system. What makes ARB inhibitors different is that they act on the receptor to which angiotensin II binds. A receptor is a molecule on the surface of a cell that joins with other molecules to perform a specific action.
A receptor and angiotensin II can be compared to locking a door. When the key (angiotensin II) joins the lock (receptor site), it causes an action - the locking of the door. The door closing would be similar to the way in which angiotensin II causes the vessels to constrict. When the lock, or receptor site to angiotensin II is blocked, the door, or blood vessels, would remain open because the two are not able to interact. The blood vessels are able to dilate making it easier for the blood to flow through the vessels and reduce the blood pressure.
In addition to reducing blood pressure, this medication increases the release of water and sodium through the form of urine for patients with poor kidney function. This occurs through ARB blocking the effects of aldosterone, a hormone that retains salt and water.
Here is a helpful handout from BC Renal Agency to help you learn about this medication!